1. Field of the Invention
The present invention relates to apparatus and systems which may be utilized to mass-produce semiconductor devices. In particular, this invention pertains to the production of amorphous semiconductor devices by continuous, as opposed to batch, processing.
2. Description of the Prior Art
Crystalline materials which feature a regular lattice structure were formerly considered essential in the manufacture of reliable semiconductor devices. While solar cells, switches and the like having favorable characteristics continue to be so manufactured, it is recognized that preparation of crystalline materials introduces substantial costs into the semiconductor industry. Single crystal silicon and the like must be produced by expensive and time-consuming methods. Czochralski and like crystal growth techniques involve the growth of an ingot which must then be sliced into wafers and are thus inherently batch processing concepts.
Recent developments in the field of devices formed of amorphous semiconductor materials offer a potentially significant reduction in production costs. In particular, solar cell technology, which is dependent upon the production of a large number of devices to comprise a panel, is critically affected by processing economies. The feasibility of semiconductor devices produced by amorphous, as opposed to crystalline, materials is disclosed, for example, in U.S. Pat. No. 4,217,374 of Ovshinsky and Izu for "Amorphous Semiconductors Equivalent to Crystalline Semiconductors". A silicon solar cell produced by successive glow discharge deposition of layers of various conductivities and dopings and its process of manufacture are described in U.S. patent application Ser. No. 887,353 of Ovshinsky and Madan filed Mar. 16, 1978 for "Amorphous Semiconductors Equivalent to Crystalline Semiconductors", now U.S. Pat. No. 4,226,898. Both of these prior art patents are hereby incorporated by reference as representative of amorphous semiconductor technology.
The feasibility of amorphous devices becomes apparent in light of the drawbacks inherent in production of crystalline devices. In addition to the aforementioned inherently "batch" nature of crystal growth, a substantial amount of the carefully grown material is lost in the sawing of the ingot into a plurality of useable wafers. Substantial surface finishing and processing effort is often required thereafter.
Generally, the production of amorphous devices utilizes batch methods. As in the case of crystalline devices, such production methods impair the economic feasibility of amorphous devices such as solar cells by introducing "dead time" during which valuable equipment sits idle. Recently, efforts have been directed to the possibility of producing amorphous semiconductor devices by continuous processes. U.S. patent application of Izu, Canella and Ovshinsky for "Continuous Amorphous Solar Cell Production System" Ser. No. 240,493, filed 3-16-81 as the property of the assignee herein, discloses a system and method for the continuous production of solar cells of amorphous material. In that application, there is generally disclosed a system for advancing a weblike substrate of material through a plurality of modules to produce a plurality of solar cells.